Electrode-forming composition and additive

Abstract

Provided is a composition for electrode formation which allows improved storage stability as a result of suppressing thickening and gelation, by using a simple method, and which allows increased concentration of solid components. The composition contains a heterocycle-containing compound, a positive electrode active material, a binder, and a solvent. The heterocycle-containing compound is represented by formula (1). (Each Ra is independently a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an optionally substituted C1-6 alkyl group, an optionally substituted C2-6 alkenyl group, or an optionally substituted C6-12 aryl group; each L is independently a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond; and each Xa is independently a hydrogen atom, a lithium atom, a sodium atom, an optionally substituted C1-6 alkyl group, or an optionally substituted C6-12 aryl group.)

Description

Technical Field

[0001] The present invention relates to a composition for electrode formation and an additive.

Background Art

[0002] Lithium ion secondary batteries contribute to the miniaturization and weight reduction of mounted electronic devices because of their high energy density per unit weight and volume. In recent years, as part of efforts towards zero emissions in automobiles, the spread of electric vehicles has been accelerating, and further reduction of resistance, extension of lifespan, increase in capacity, improvement of safety, and cost reduction have been demanded.

[0003] Lithium ion batteries generally have a three-layer structure of a positive electrode, a separator, and a negative electrode, including an electrolyte solution. The positive electrode and the negative electrode are manufactured, for example, by applying an electrode slurry in which an active material, a conductive material, and a binder are mixed to a current collector. Currently, as a method for manufacturing a negative electrode, a process of applying a negative electrode slurry to a copper foil serving as a current collector and drying it is the mainstream. As a method for manufacturing a positive electrode, a process of preparing a positive electrode slurry using an organic solvent such as N-methylpyrrolidone as a solvent and applying it to an aluminum foil serving as a current collector is the mainstream.

[0004] As positive electrode active materials for lithium ion secondary batteries, inorganic compounds such as transition metal oxides containing alkali metals and transition metal chalcogens are known as those capable of obtaining a battery voltage of around 4V. Among these, in order to obtain a high-capacity lithium ion secondary battery, a highly alkaline positive electrode active material containing a large amount of nickel or manganese is used.

[0005] For example, Li x The high-nickel positive electrode active material typified by NiO2 has a high discharge capacity and is an attractive positive electrode material. However, on its surface, there are alkali components such as LiOH, Li2O, LiHCO3, and Li2CO3 generated by proton exchange reactions with raw material residues or moisture, or reactions with moisture or carbon dioxide gas in the air.

[0006] When such a positive electrode active material is used, there is a problem that the electrode slurry gradually loses fluidity by thickening or gelling. When the electrode slurry loses fluidity, it becomes difficult to obtain a uniform coating thickness, and in some cases, coating cannot be performed, resulting in waste of materials.

[0007] The main cause of this is thought to be that in the process of manufacturing the positive electrode, the alkali component present on the surface of the positive electrode active material promotes the dehydrofluorination reaction of a fluorine-based binder typified by PVdF having a vinylidene fluoride structure used as a binder in the presence of a small amount of moisture.

[0008] Furthermore, the alkali component increases the resistance of the battery by corroding the aluminum foil generally used as the current collector foil of the positive electrode. In addition, the above alkali component may react with the electrolyte in the battery, increasing the resistance of the battery and deteriorating its lifespan.

[0009] The above-mentioned thickening and gelling can be suppressed by handling the raw materials and the electrode slurry in a dry environment and controlling the moisture content. However, large-scale equipment is required in a series of mass production processes from the preparation of the electrode slurry to the manufacture of the battery, and the cost increase and environmental load increase due to the use of a large amount of electricity become problems.

[0010] To solve this problem, for example, Patent Document 1 discloses a technique for suppressing the gelling of an electrode slurry (positive electrode material slurry) by preparing the electrode slurry so as not to exhibit strong alkalinity even when dispersed in water. However, preparing the electrode slurry so as not to exhibit strong alkalinity by the method described in Patent Document 1 not only requires strict pH control, but also requires a process of once dispersing the positive electrode active material in water, filtering it from the dispersion liquid to take out the positive electrode active material, and then drying it. As a result, it causes the complexity of the work and the reduction of the yield. In addition, the above-mentioned process may also cause a decrease in the performance of the positive electrode active material itself.

[0011] In Patent Document 2, a technique of suppressing thickening and gelation is reported by using a compound such as polyethylene oxide with ultra-high molecular weight (weight average molecular weight of 2.2 million or more) to restrain water through interaction with water (e.g., hydrogen bond) and suppressing the reaction between the alkaline component of the positive electrode active material and water. However, polymers with ultra-high molecular weight and strong thickening effect require time and cost for uniform dissolution treatment in a solvent, and there are handling problems such as difficulty in obtaining a high-concentration solution. In addition, since the above-mentioned ultra-high molecular weight polymer has a high ability to restrain water, conversely, there is a concern that the polymer itself may bring in water, and strict management of prior drying is required to prevent this.

[0012] In Patent Documents 3 and 4, it is proposed to add an organic acid or an inorganic acid in order to suppress the gelation of an electrode slurry (positive electrode mixture slurry) in the positive electrode of a lithium-ion secondary battery. In Patent Document 3, maleic acid, citraconic acid, and malonic acid are used in the positive electrode mixture, and in Patent Document 4, acetic acid, phosphoric acid, sulfuric acid, etc. are used in the electrode slurry (positive electrode paste). However, a large amount of addition is required to neutralize the alkali with an acid, and as a result, there is a risk of reducing the energy density of the battery and increasing the resistance of the battery. In addition, there is also a problem that the acid corrodes the device for manufacturing the electrode.

[0013] In Patent Document 5, a method is reported in which the positive electrode active material is treated with fluorine gas to immobilize residual LiOH as LiF, thereby preventing gelation and suppressing gas generation. However, fluorine gas is highly toxic and difficult to handle, and LiF generated as a by-product increases the internal resistance of the battery, reduces the capacity, and the capacity also decreases due to corrosion of the positive electrode active material by fluorine gas. Furthermore, there is a problem that residual fluorine reacts with trace amounts of moisture present in the active material or the electrolyte to generate hydrogen fluoride, which easily causes cycle degradation.

[0014] In Patent Document 6, it has been reported that unreacted lithium hydroxide and impurities derived from raw materials are removed by washing with an aqueous solution containing a lithium salt. However, there are problems in terms of the increased environmental load due to the wastewater generated during washing and the cost associated with the treatment of the wastewater.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0016] In view of such circumstances, the present invention aims to provide a composition for forming an electrode that can suppress the thickening and gelation of an electrode slurry by a simple method, improve the storage stability, increase the solid content concentration, and suppress the deterioration of a battery, as well as an additive effective in suppressing the gelation of the composition for forming an electrode.

Means for Solving the Problems

[0017] As a result of intensive studies to achieve the above object, the present inventors have found that by adding a specific heterocyclic compound having two 5-membered heterocycles each having two heteroatoms in the same ring to a composition for forming an electrode containing at least a positive electrode active material, a binder, and a solvent, thickening and gelation of the composition can be suppressed, and storage stability can be enhanced. Further, an electrode produced using the composition for forming an electrode of the present invention can suppress deterioration in a battery due to an alkaline component and can also enhance battery characteristics.

[0018] That is, the present invention provides the following composition for forming an electrode and an additive. 1. A composition for forming an electrode containing a heterocyclic compound, a positive electrode active material, a binder, and a solvent, wherein the heterocyclic compound is a composition for forming an electrode represented by the following formula (1). [Chemical formula] (In the formula, R a each independently represents a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, L each independently represents a single bond, a carbonyl group, an ether bond, an ester bond or an amide bond, X a each independently represents a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent.) 2. The composition for forming an electrode according to 1, wherein each of the above X a independently represents a hydrogen atom, a lithium atom, a sodium atom or a phenyl group. 3. The composition for forming an electrode according to 1, wherein L is a single bond, and each of R a independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent. 4. In the above formula (1), Ra and X a The substituent(s) of a is at least one selected from the group consisting of a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, and a carboxylic acid chloride group. The electrode-forming composition of 1. 5. The electrode-forming composition of 1, wherein the heterocyclic compound is represented by the following formula (1-1). [Chemical formula] 6. The electrode-forming composition according to any one of 1 to 5, further comprising a conductive aid. 7. The electrode-forming composition according to any one of 1 to 6, wherein the positive electrode active material contains 30 mass% or more of S, Fe, or Ni. 8. The electrode-forming composition according to any one of 1 to 7, further comprising a dispersant, and the dispersant is a polymer containing a pyrrolidone structure or a nitrile group. 9. The electrode-forming composition of 8, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile. 10. The electrode-forming composition according to any one of 1 to 9, wherein the content of the heterocyclic compound is 0.001 to 0.5 mass% in the solid content. 11. An additive for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent, the additive comprising a heterocyclic compound represented by the following formula (1). [Chemical formula] (In the formula, R a each independently represents a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, L each independently represents a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond, X aEach independently is a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent.) 12. The additive 11 which is a gelation inhibitor. 13. An additive solution for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent, the additive solution comprising an additive composed of a heterocyclic compound represented by the following formula (1) and a solvent.

Chemical formula

Advantages of the Invention

[0019] The electrode-forming composition of the present invention is less likely to thicken or gel and has high storage stability, and can be suitably used for forming a positive electrode of an energy storage device. When an energy storage device equipped with an electrode produced using the composition is manufactured, advantages such as improvement in quality and yield due to improvement in the storage stability of the composition, cost reduction and reduction of environmental load due to high concentration of the solid content, and suppression of deterioration in the battery due to the alkaline component are expected, and it can contribute to reduction of the manufacturing cost of the energy storage device and improvement of battery characteristics.

[0020] Incidentally, although the mechanisms of the above thickening and gelling, as well as the mechanism of the manifestation of the inhibitory effect, are not clear, in the present invention, it is considered that a protective film is formed on the surface of the alkali component by adding a specific heterocyclic compound to the composition for electrode formation. This protective film suppresses the reaction between the alkali component and the binder, particularly the fluorine-based binder. As a result, it is considered that the thickening and gelling of the composition can be suppressed, and the storage stability is improved. By suppressing the thickening and gelling of the composition for electrode formation, the dispersibility of the solid components such as the positive electrode active material and the conductive assistant becomes good, so that a homogeneous positive electrode layer can be formed. In addition, it is also possible to increase the concentration of the solid component in the electrode slurry, and the cost and environmental load of manufacturing the energy storage device can be reduced. Furthermore, corrosion of the aluminum foil generally used as the current collector foil derived from the alkali component and deterioration of the battery characteristics due to the reaction with the electrolytic solution can be suppressed. However, these are estimations, and the present invention is not construed as being limited to these mechanisms.

Embodiments for Carrying Out the Invention

[0021] The composition for electrode formation of the present invention is a composition for electrode formation containing a heterocyclic compound, a positive electrode active material, a binder, and a solvent, wherein the heterocyclic compound is represented by the following formula (1).

[0022]

Chemical formula

[0023] R a Examples of the alkyl group having 1 to 6 carbon atoms represented by a may be linear, branched or cyclic. Specific examples thereof include linear or branched alkyl groups having 1 to 6 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n-pentyl group, n-hexyl group; and cyclic alkyl groups having 3 to 6 carbon atoms such as cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group.

[0024] R a Examples of the alkenyl group having 2 to 6 carbon atoms represented by a include ethenyl group, n-1-propenyl group, n-2-propenyl group, 1-methylethenyl group, n-1-butenyl group, n-2-butenyl group, n-3-butenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-ethylethenyl group, 1-methyl-1-propenyl group, 1-methyl-2-propenyl group, n-1-pentenyl group and the like.

[0025] R a Examples of the aryl group having 6 to 12 carbon atoms represented by a include phenyl group, tolyl group, 1-naphthyl group, 2-naphthyl group and the like.

[0026] The above R amay have a substituent. Examples of the substituent include a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, a thiol group, and the like. Examples of the alkoxysilyl group include a trimethoxysilyl group, a dimethoxymethylsilyl group, a methoxydimethylsilyl group, a triethoxysilyl group, a diethoxymethylsilyl group, an ethoxydimethylsilyl group, and the like. In the present invention, a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, and a carboxylic acid chloride group are preferable. The above R a When having a substituent, the number thereof is preferably 1 to 6, more preferably 1 to 3.

[0027] The above R a is preferably a hydrogen atom, a hydroxy group, a thiol group, and an optionally substituted alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom and an optionally substituted alkyl group having 1 to 6 carbon atoms, even more preferably a hydrogen atom and an alkyl group having 1 to 6 carbon atoms, and still more preferably a hydrogen atom and a methyl group.

[0028] L is preferably a single bond, an ester bond, or an amide bond, and more preferably a single bond.

[0029] X a The alkyl group having 1 to 6 carbon atoms represented by may be linear, branched, or cyclic. Specific examples thereof include linear or branched alkyl groups having 1 to 6 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an n-pentyl group, and an n-hexyl group; and cyclic alkyl groups having 3 to 6 carbon atoms such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0030] X a Examples of the aryl group having 6 to 12 carbon atoms represented by include a phenyl group, a tolyl group, a 1-naphthyl group, and a 2-naphthyl group.

[0031] The above X a may have a substituent. Examples of the substituent include a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, a carboxylic acid chloride group, a thiol group, and the like. Examples of the alkoxysilyl group include a trimethoxysilyl group, a dimethoxymethylsilyl group, a methoxydimethylsilyl group, a triethoxysilyl group, a diethoxymethylsilyl group, an ethoxydimethylsilyl group, and the like. In the present invention, a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, and a carboxylic acid chloride group are preferred. The above X a When having a substituent, the number thereof is preferably 1 to 6, more preferably 1 to 3.

[0032] The above X a is preferably a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms, more preferably a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 3 carbon atoms, or an aryl group having 6 to 8 carbon atoms, particularly preferably a hydrogen atom, a lithium atom, a sodium atom, a methyl group, and a phenyl group, and even more preferably a hydrogen atom, a lithium atom, a sodium atom, and a phenyl group.

[0033] As the heterocyclic compound represented by the above formula (1), a heterocyclic compound represented by the following formula (1a) is preferred.

[0034]

Chemical formula

[0035] Specific examples of the above heterocyclic compound include heterocyclic compounds represented by the following formulas (1-1) to (1-4). Among these, in the present invention, the heterocyclic compound (Bis(3-methyl-1-phenyl-5-pyrazolone)) represented by the following formula (1-1) is preferred.

[0036]

Chemical formula

[0037] The content of the above heterocyclic compound is preferably 0.001 to 4% by mass in the solid content, more preferably 0.001 to 2% by mass, still more preferably 0.001 to 0.5% by mass, further preferably 0.001 to 0.3% by mass, and particularly preferably 0.001 to 0.2% by mass. Further, a still more preferable lower limit of the content of the above heterocyclic compound is 0.01% by mass in the solid content. By setting the content of the heterocyclic compound within the above range, the adhesion between the current collector and the electrode layer can be improved, and the battery characteristics of the obtained battery can also be maintained. In the present invention, the solid content means components other than the solvent constituting the composition (hereinafter the same).

[0038] As the positive electrode active material, those containing 30% by mass or more of S, Fe, or Ni are preferred in terms of further improving the battery capacity, reducing the amount of rare metals used, and being low-cost. In the present invention, considering further reducing the amount of rare metals used and obtaining a battery with a longer lifespan, those containing 35% by mass or more of Fe or Ni are more preferred, and those containing 45% by mass or more are still more preferred. Also, the upper limit is not particularly limited, but is usually 65% by mass or less. As such a positive electrode active material, those satisfying the above conditions can be appropriately selected and used from various active materials conventionally used for electrodes of energy storage devices such as secondary batteries. For example, in the case of a lithium secondary battery or a lithium ion secondary battery, a chalcogen compound capable of adsorbing and desorbing lithium ions or a lithium ion-containing chalcogen compound, a polyanion-based compound, sulfur alone and its compounds, etc. can be used.

[0039] Examples of the lithium ion-containing chalcogen compound include, for example, LiNiO2, Li x Ni y M 1-y O2 (M represents at least one metal element selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, 0.05 ≦ x ≦ 1.10, 0.3 ≦ y ≦ 1.0), Li a Ni (1-x-y) Co x M 1 y M 2 z X w O2 (M 1 is at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, B, Zr, W, and V, 1.00 ≦ a ≦ 1.50, 0.00 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.50, 0.000 ≦ z ≦ 0.020, 0.000 ≦ w ≦ 0.020), etc. Examples of the polyanion compound include, for example, LiFePO 4、 Li a Mn b Fe c D d PO4 (1.00 ≦ a ≦ 1.15, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.99, 0.00 ≦ d ≦ 0.10, and D is selected from Co, Mn, Ti, Cr, V, Al, Sn, Pb, and Zn, and at least a part has an olivine structure), etc. Examples of the sulfur compound include sulfur, Li2S, FeS2, TiS2, MoS2, rubianic acid, etc. These cathode active materials can be used alone or in combination of two or more.

[0040] In the present invention, among the above cathode active materials, Li a Ni (1-x-y) Co x M 1 y M 2 z X w O2 (M 1is at least one selected from the group consisting of Mn and Al, M 2 represents at least one selected from the group consisting of Zr, Ti, Mg, W, and V, and 1.00 ≦ a ≦ 1.50, 0.00 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.50, 0.000 ≦ z ≦ 0.020, 0.000 ≦ w ≦ 0.020) is preferred. These active materials can be used alone or in combination of two or more.

[0041] The content of the above positive electrode active material is preferably 88.0 to 99.949% by mass, more preferably 88.0 to 99.899% by mass, and even more preferably 95.0 to 99.0% by mass in the solid content.

[0042] As the above binder, it can be appropriately selected from known materials and is not particularly limited. Specific examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene; copolymers containing at least one monomer selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene, and non-aqueous binders such as polyimide, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, polyethylene, and polypropylene. In the present invention, from the viewpoint of improving the storage stability of the composition, it is preferable to use a fluorine-based binder. Further, the above fluorine-based binder is preferably modified with a polar functional group such as a carboxy group or a hydroxy group. The presence or absence of a distinct peak detected in the range of 10 to 15 ppm in the measurement by a nuclear magnetic resonance apparatus (NMR apparatus) can confirm the above polar functional group. The above binder can be used alone or in combination of two or more.

[0043] The weight average molecular weight (Mw) of the above binder is usually about 600,000 to 3,000,000, preferably 700,000 to 2,000,000, more preferably 700,000 to 1,500,000, from the viewpoint of improving the adhesion between the current collector and the electrode layer. The weight average molecular weight is a polystyrene equivalent value determined by gel permeation chromatography (GPC).

[0044] From the viewpoints of suppressing cost and obtaining a high energy density, the content of the above binder is preferably 0.05 to 8% by mass, more preferably 0.05 to 5% by mass, even more preferably 0.05 to 4% by mass, still more preferably 0.1 to 3% by mass, particularly preferably 0.2 to 2% by mass, and most preferably 0.3 to 1.5% by mass in the solid content.

[0045] The composition for forming an electrode of the present invention may further contain a conductive aid in order to improve electrical conductivity more favorably. Examples of the conductive aid include carbon materials such as graphite, carbon black, acetylene black (AB), vapor-grown carbon fiber, carbon nanotube (CNT), carbon nanohorn, and graphene, and conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene. The above conductive aid can be used alone or in combination of two or more.

[0046] When the above conductive aid is included, its content is not particularly limited, but is preferably 0.05 to 5% by mass, more preferably 0.05 to 4% by mass, even more preferably 0.1 to 3% by mass, and still more preferably 0.2 to 2% by mass in the solid content. By setting the content of the conductive aid within the above range, good electrical conductivity can be obtained.

[0047] The composition for forming an electrode of the present invention may further contain a dispersant in order to improve the dispersibility of the above-mentioned active material and conductive assistant. The above-mentioned dispersant can be appropriately selected from those conventionally used as dispersants for conductive carbon materials such as CNTs. However, from the viewpoint of stability in the battery, it is preferable to contain a nonionic polymer. Examples of the above-mentioned nonionic polymer include polyvinylpyrrolidone (PVP), and polymers having at least one group selected from the group consisting of a nitrile group, a hydroxy group, a carbonyl group, an amino group, a sulfonyl group, and an ether group. Specific examples of the above-mentioned polymer include polyvinyl alcohol, polyacrylonitrile, polylactic acid, polyester, polyimide, polyphenyl ether, polyphenyl sulfone, polyethyleneimine, polyaniline, and the like. In the present invention, a polymer containing a pyrrolidone structure or a nitrile group is preferable, and polyvinylpyrrolidone and polyacrylonitrile are more preferable. The above-mentioned dispersant can be used alone or in combination of two or more.

[0048] When the above-mentioned dispersant is included, its content is not particularly limited, but is preferably 0.001 to 0.5% by mass, more preferably 0.001 to 0.3% by mass, and even more preferably 0.001 to 0.2% by mass in the solid content. Further, a more preferable lower limit of the content of the above-mentioned dispersant is 0.01% by mass in the solid content. Also, considering the adhesion between the obtained electrode layer and the current collector, the total amount of the above-mentioned heterocyclic compound and the above-mentioned dispersant is preferably 0.001 to 1% by mass, more preferably 0.01 to 1% by mass in the solid content.

[0049] The electrode-forming composition of the present invention contains a solvent. The solvent is not particularly limited as long as it is conventionally used for preparing an electrode-forming composition. For example, water; ethers such as tetrahydrofuran (THF), diethyl ether, 1,2-dimethoxyethane (DME); halogenated hydrocarbons such as methylene chloride, chloroform, 1,2-dichloroethane; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP); ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, t-butanol; aliphatic hydrocarbons such as n-heptane, n-hexane, cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene; glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether; glycols such as ethylene glycol, propylene glycol; carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate; and organic solvents such as γ-butyrolactone, dimethyl sulfoxide (DMSO), dioxolane, sulfolane. These solvents can be used alone or in combination of two or more.

[0050] In addition, the above binder may be dissolved or dispersed in these solvents and used as needed. Suitable solvents in this case include water, NMP, DMSO, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, THF, dioxolane, sulfolane, DMF, DMAc, etc. They may be appropriately selected according to the type of binder. In the case of a water-insoluble binder such as PVdF, NMP is suitable, and in the case of a water-soluble binder, water is suitable.

[0051] The solid content concentration of the composition for forming an electrode of the present invention is appropriately set in consideration of the coatability of the composition, the thickness of the electrode to be formed, etc., but is usually about 60 to 92% by mass, preferably about 65 to 90% by mass, and more preferably about 70 to 85% by mass.

[0052] The viscosity of the composition for forming an electrode of the present invention is appropriately set in consideration of the coating method, the thickness of the electrode to be formed, etc., but is usually about 100 to 2,000,000 mPa·s, preferably about 300 to 1,000,000 mPa·s, and more preferably about 400 to 800,000 mPa·s. The above viscosity is a value measured at 25°C with an E-type viscometer.

[0053] The composition for forming an electrode of the present invention can be obtained by mixing the above-described respective components. When the additive (heterocyclic compound-containing compound), the positive electrode active material, and optional components other than the binder of the present invention are included, the additive and the positive electrode active material may be mixed together with the optional components, or after the two components are mixed in advance, they may be mixed with the optional components. In any method, the effects of the present invention can be exhibited.

[0054] The electrode of the present invention includes an electrode layer made of the composition for forming an electrode described above on at least one surface of a substrate that is a current collector. As a method for forming the electrode layer on the substrate, there is a method of coating the prepared composition for forming an electrode on the substrate to form a coating film, and then drying this. This method is not particularly limited, and various conventionally known methods can be used. Specific examples of the coating method include various printing methods such as offset printing and screen printing, blade coating method, dip coating method, spin coating method, bar coating method, slit coating method, inkjet method, die coating method, etc.

[0055] Also, when drying the coating film, either natural drying or heat drying may be employed, but heat drying is preferred from the viewpoint of production efficiency. When heat drying is carried out, the temperature is preferably about 50 to 400°C, and more preferably about 70 to 150°C.

[0056] Examples of the substrate used for the above electrode include metal substrates such as platinum, gold, iron, stainless steel, copper, aluminum, and lithium, alloy substrates composed of any combination of these metals, oxide substrates such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO), or carbon substrates such as glassy carbon, pyrolytic graphite, and carbon felt. In particular, the thickness of the substrate is not particularly limited, but in the present invention, 1 to 100 μm is preferable, 3 to 30 μm is preferable, and 5 to 25 μm is most preferable.

[0057] The film thickness of the above electrode layer is not particularly limited, but is preferably about 0.01 to 1,000 μm, more preferably about 5 to 300 μm. When the electrode layer is used as an electrode alone, its film thickness is preferably 10 μm or more.

[0058] The electrode may be pressed as necessary. As the pressing method, generally adopted methods can be used, but in particular, the die pressing method and the roll pressing method are preferable. The pressing pressure is not particularly limited, but 1 kN / cm or more is preferable, 2 kN / cm or more is preferable, and 5 kN / cm or more is more preferable. The upper limit of the above pressing pressure is not particularly limited, but 50 kN / cm or less is preferable.

[0059] The secondary battery of the present invention includes the above-described electrode. More specifically, it includes at least a pair of positive and negative electrodes, a separator interposed between these electrodes, and an electrolyte, and the positive electrode is composed of the above-described electrode. Other constituent members of the battery element may be appropriately selected from conventionally known ones and used.

[0060] Examples of the material used for the above separator include glass fiber, cellulose, porous polyolefin, polyamide, and polyester.

[0061] The above electrolyte may be either liquid or solid, and may be either aqueous or non-aqueous. However, from the perspective of easily exhibiting sufficient practical performance, an electrolytic solution composed of an electrolyte salt, a solvent, etc. can be preferably used.

[0062] Examples of the above electrolyte salts include lithium salts such as LiPF6, LiBF4, LiN(SO2F) 2、 LiN(C2F5SO2)2, LiAsF6, LiSbF6, LiAlF4, LiGaF4, LiInF4, LiClO4, LiN(CF3SO2)2, LiCF3SO3, LiSiF6, LiN(CF3SO2),(C4F9SO2), etc.; metal iodides such as LiI, NaI, KI, CsI, CaI2; iodide salts of quaternary imidazolium compounds; iodide salts and perchlorate salts of tetraalkylammonium compounds; metal bromides such as LiBr, NaBr, KBr, CsBr, CaBr2, etc. These electrolyte salts can be used alone or in combination of two or more.

[0063] The above solvent is not particularly limited as long as it does not cause corrosion or decomposition to the substances constituting the battery and deteriorate the performance, and can dissolve the above electrolyte salt. For example, as non-aqueous solvents, cyclic esters such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, etc.; ethers such as tetrahydrofuran, dimethoxyethane, etc.; chain esters such as methyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.; nitriles such as acetonitrile, etc. are used. These solvents can be used alone or in combination of two or more.

[0064] Also, as solid electrolytes, inorganic solid electrolytes such as sulfide-based solid electrolytes and oxide-based solid electrolytes, and organic solid electrolytes such as polymer-based electrolytes can be preferably used. By using these solid electrolytes, an all-solid-state battery that does not use an electrolytic solution can be obtained.

[0065] Examples of the sulfide solid electrolyte include Li2S-SiS2-lithium compounds (where the lithium compound is at least one selected from the group consisting of Li3PO 4、 LiI and Li4SiO4) 、 Li2S-P2O 5、 Li2S-B2S 5、 Examples thereof include thiolsilicon-based materials such as Li2S-P2S5-GeS2.

[0066] Examples of the oxide solid electrolyte include oxides having a garnet-type structure, such as Li5La3M2O 12 (M = Nb, Ta), Li7La3Zr2O 12 , oxygenate compounds based on the γ-Li3PO4 structure generally referred to as LISICON, perovskite-type, Li 3.3 PO 3.8 N 0.22 , sodium / alumina, and the like. Examples of the polymer solid electrolyte include polyethylene oxide-based materials and polymer compounds obtained by polymerizing or copolymerizing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. The polymer solid electrolyte may contain a supporting salt and a plasticizer.

[0067] Examples of the supporting salt contained in the polymer solid electrolyte include lithium (fluorosulfonylimide), and examples of the plasticizer include succinonitrile.

[0068] A battery manufactured using the composition for forming an electrode of the present invention has high battery characteristics even when the amount of the fluorine binder is small as compared with a general secondary battery.

[0069] The form of the secondary battery and the type of electrolyte are not particularly limited, and any form such as a lithium ion battery, a nickel hydrogen battery, a manganese battery, an air battery, etc. may be used, but a lithium ion battery is preferred. The lamination method and the production method are also not particularly limited.

[0070] When applying to a coin type, the electrode of the present invention described above may be punched out into a predetermined disc shape and used. For example, in a lithium ion secondary battery, one electrode is installed on a lid in which a washer and a spacer of a coin cell are welded, and on top of it, a separator of the same shape impregnated with an electrolytic solution is overlaid. Further, from above, the electrode of the present invention is overlaid with the electrode layer facing down, a case and a gasket are placed, and it can be manufactured by sealing with a coin cell caulking machine.

[0071] The present invention also provides an additive comprising a heterocyclic compound represented by the following formula (1) as an additive for an electrode-forming composition containing a positive electrode active material, a binder and a solvent. The above additive can be suitably used as a gelation inhibitor for an electrode-forming composition containing a positive electrode active material, a binder and a solvent.

[0072]

Chemical formula

[0073] In formula (1), R a and Xa Specific examples thereof are the same as those exemplified in the description of the composition for electrode formation.

[0074] Also, with respect to the positive electrode active material, binder, and solvent of the composition for electrode formation, they are the same as those described in the above description.

[0075] Furthermore, the present invention provides an additive solution for a composition for electrode formation containing a positive electrode active material, a binder, and a solvent, which is an additive solution comprising an additive composed of a heterocyclic compound represented by the following formula (1) and a solvent. By using the additive solution of the present invention, it becomes easier to mix the above additive with the composition for electrode formation.

[0076]

Chemical formula

[0077] In formula (1), specific examples of R a and X a are the same as those exemplified in the description of the composition for electrode formation.

[0078] The above gelation inhibitor solution is preferably one in which each of the above compounds is dissolved or dispersed in a solvent, and more preferably one in which each is dissolved in a solvent.

[0079] Examples of solvents that can be used include the same ones as those exemplified in the description of the electrode-forming composition. In the present invention, among them, NMP, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate can be preferably used.

[0080] Also, regarding the positive electrode active material and the binder of the electrode-forming composition, they are the same as those described in the above explanation.

[0081] The solid content concentration of the gelation inhibitor solution of the present invention is appropriately set in consideration of the saturation solubility in the solvent, storage stability, etc., but is usually about 1 to 60% by mass, preferably about 3 to 55% by mass, and more preferably about 3 to 50% by mass.

Examples

[0082] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. The apparatuses used are as follows.

[0083] (1) Rotating and revolving mixer: manufactured by Shinchi Co., Ltd., Awatori Renkitaro, atmospheric pressure type ARE-310 (2) Drive booth: manufactured by Nippon Spindle Manufacturing Co., Ltd. (3) E-type viscometer: manufactured by Toki Sangyo Co., Ltd., VISCOMETER TV-22, measurement temperature: 25°C, rotor: 1°34’×R24, the viscosity 5 minutes after the start of measurement was adopted under the measurement conditions.

[0084] Also, the raw materials used, etc. are as follows. <Active material> NCA: Lithium nickelate (LiNi 0.88 Co 0.11 Al 0.01 O2, NCA-034H, Ni ratio: 55% by mass), manufactured by Ecopro Co., Ltd. <Fluorine-based binder> Solef-5130: Polyvinylidene fluoride (PVdF), manufactured by SOLVAY Co., Ltd. <Conductive Aid> AB: Denka Black (registered trademark) Li100 (high-purity acetylene black), manufactured by Denka Co., Ltd. <Solvent> NMP: Manufactured by Nippon Refining Co., Ltd. <Additive A> [Additives used in the examples] A1: Bis(3-methyl-1-phenyl-5-pyrazolone), manufactured by Tokyo Chemical Industry Co., Ltd.

Chemical formula

Chemical formula

[0085] · Preparation of the composition for the positive electrode (electrode slurry) [Example 1-1, Comparative Examples 1-1 to 1-7] For each additive, a 5 mass% NMP solution was prepared. A 7 mass% NMP solution of PVdF was prepared. Inside the dry booth, the positive electrode active material, binder solution, conductive aid, additive solution, NMP, and water were mixed to achieve the composition ratios shown in Table 1, and the electrode slurry was obtained by mixing using a rotation and revolution mixer. The total amount of the prepared slurries was 20 g each, the solid content was 80 mass%, and the solvent composition of the slurry was adjusted to NMP / H2O = 97 / 3 (mass ratio). The above water was added to intentionally create a state where the water content in the slurry was high.

[0086] Regarding the slurry obtained above, viscosity measurement was carried out using an E-type viscometer immediately after preparation. Also, after storage at 40 °C for 24 hours, the presence or absence of gelation was visually confirmed. For those that did not gel, viscosity measurement was similarly carried out using an E-type viscometer to confirm the presence or absence of thickening and gelation tendency, and the determination was made based on the following criteria. These evaluations are also summarized in Table 1. 《Judgment Criteria》 A: Those that did not gel B: Those in which the composition gelled and cannot be used for electrode formation

[0087]

Table 1

[0088] From the results in Table 1 above, it was confirmed that in the composition for electrode formation of the present invention to which a specific heterocyclic compound was added, thickening and gelation were suppressed and the storage stability was improved.

Claims

1. An electrode-forming composition comprising a heterocycle-containing compound, a positive electrode active material, a binder, and a solvent, The heterocycle-containing compound is represented by the following formula (1): 【Chemistry 1】 (In the formula, R a each independently represents a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, Each L is independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond; X a are each independently a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent.

2. Above X a 2. The electrode-forming composition according to claim 1, wherein each of the groups independently represents a hydrogen atom, a lithium atom, a sodium atom, or a phenyl group.

3. The above L is a single bond, and R a 2. The electrode-forming composition according to claim 1, wherein each of the groups independently represents a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms.

4. In the above formula (1), R a and X a 2. The electrode-forming composition according to claim 1, wherein the substituent of is at least one selected from the group consisting of a carboxy group, a hydroxy group, an aldehyde group, an ester group, a ketone group, an amino group, a phenyl group, a halogen atom, an alkoxysilyl group, an epoxy group, and a carboxylic acid chloride group.

5. 2. The electrode-forming composition according to claim 1, wherein the heterocycle-containing compound is represented by the following formula (1-1): 【Chemistry 2】

6. The electrode-forming composition according to claim 1 , further comprising a conductive assistant.

7. 2. The electrode-forming composition according to claim 1, wherein the positive electrode active material contains 30 mass % or more of S, Fe or Ni.

8. 2. The electrode-forming composition according to claim 1, further comprising a dispersant, the dispersant being a polymer containing a pyrrolidone structure or a nitrile group.

9. 9. The electrode-forming composition according to claim 8, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile.

10. 10. The electrode-forming composition according to claim 1, wherein the content of the heterocycle-containing compound is 0.001 to 0.5% by mass based on the solid content.

11. An additive for an electrode-forming composition containing a positive electrode active material, a binder, and a solvent, the additive comprising a heterocycle-containing compound represented by the following formula (1): 【Chemistry 3】 (In the formula, R a each independently represents a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, Each L is independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond; X a are each independently a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent.

12. The additive of claim 11 which is a gelation inhibitor.

13. An additive solution for an electrode-forming composition comprising a positive electrode active material, a binder, and a solvent, the additive solution comprising a heterocycle-containing compound represented by the following formula (1): An additive solution comprising an additive and a solvent. 【Chemistry 4】 (In the formula, R a each independently represents a hydrogen atom, a carboxy group, a hydroxy group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent, an alkenyl group having 2 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent, Each L is independently a single bond, a carbonyl group, an ether bond, an ester bond, or an amide bond; X a are each independently a hydrogen atom, a lithium atom, a sodium atom, an alkyl group having 1 to 6 carbon atoms which may have a substituent, or an aryl group having 6 to 12 carbon atoms which may have a substituent.

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